1. Technical Field
The presently disclosed subject matter relates to lighting devices for use in vehicle headlights, fog lights, and other lights for a vehicle or vehicle and traffic applications.
2. Description of the Related Art
In general, a conventional LED light source is configured to include a single LED chip and a lens portion shaped as a so-called “cannonball type” package enclosing the LED chip.
Such an LED light source has high light take-out efficiency from the light source package and is available at a low cost. However, an LED light source with the above structure cannot serve as a linear light source like a linear filament of an incandescent lamp because of its intrinsic characteristics.
Typical vehicle headlights are arranged as high as about 60 cm away from the road surface and are configured to irradiate the road in front of the vehicle from that position. This type of vehicle headlight forms a specific light distribution pattern in which the area of the road just in front of the vehicle is not so brightly illuminated while the far-away area is illuminated with a certain intensity light, i.e., a horizontally wide light distribution. In view of this, the above-described LED light source is not suitable for use as a light source in a vehicle headlight.
Consider a vehicle headlight that utilizes a parabolic reflector, for example. In this case, such a vehicle headlight can be configured to provide a passing-by light distribution (or a low beam distribution) including a cut-off area between a bright area and a dark area in order to prevent a glare light against an opposed vehicle. The above-described LED light source, however, does not have high contrast at its light emitting portion. Accordingly, it is difficult to form such a low beam distribution.
In order to solve the above-mentioned problems, specific LED light sources for headlights have been developed and are disclosed, for example, in Japanese Patent Laid-Open Publications No. 2005-093191 and No. 2005-063706 and their respective English translations, the disclosures of which are hereby incorporated in their entireties. The LED light source described has a plurality of LED light sources configured in line to form a multi-chip type LED, thereby serving as an elongated light source.
There are other problems in that the current LED light source is significantly low in intensity as compared to a halogen lamp and a high intensity discharge (HID) burner, which are used as vehicle lighting devices. In order to solve this problem, a united LED light source is composed of a plurality of the above-mentioned LED type light sources, and a required number of the thus obtained united LED light sources are combined to obtain a vehicle lighting device with a required light intensity (for example, see Japanese Patent Laid-Open Publications No. 2003-317513 and No. 2004-095479 and their respective English translations, the disclosures of which are hereby incorporated in their entireties).
Alternatively, a large sized LED chip can be used to obtain a higher intensity light for use as a headlight while decreasing the number of the LED light sources used. In this case, however, a relatively large current is required for driving such a large-sized LED chip. In addition to this, a large amount of heat may be generated from the energized LED chip. Accordingly, if such a large-sized LED chip which requires a large current is used, this type of headlight needs a large radiator (see, for example, Japanese Patent Laid-Open Publication No. 2005-209538 and its respective English translation, the disclosure of which is hereby incorporated in its entirety).
Furthermore, novel exterior designs using LED light sources are required for not only headlights, but also for various vehicle lighting devices such as rear lights, high mount stop lights, positioning lights, cornering lights, traffic lights and the like.
Conventionally, some different types of vehicle lighting devices using an LED light source are put to practical use, including a direct illumination type lighting device using an LED light source, a reflection and diffusion type lighting device using a reflector for reflecting light from the LED light source, and a diffusion type lighting device using a lens cut for diffusion.
However, technologies disclosed in Japanese Patent Laid-Open Publications No. 2005-093191 and No. 2005-063706 have problems in that part of the light emitted from respective LED chips impinges on adjacent LED chips and is prevented from being emitted outwards. This may increase light loss and lower light take-out efficiency for the LED.
In case of multi-chip type LEDs, the design and manufacturing requirements for multi-chip type LEDs may increase the entire cost related to these products. Furthermore, because multi-chip type LEDs are not typically configured as a general-purpose type lamps, but are configured to be a dedicated light source for use in headlights, the LED packages are expensive.
The structures having a plurality of united LED light sources disclosed in Japanese Patent Laid-Open Publications No. 2003-317513 and No. 2004-095479 require high level positioning accuracy and assembly accuracy for each of the light sources. Accordingly, it is difficult to suppress variation in the optical axis alignment due to the above-mentioned causes to a certain level. In order to accurately align the optical axes of the united light sources with each other, an optical axis adjustment mechanism is required for each of the LED light sources of the above configuration, resulting in a complex structure and assembly.
Furthermore, the structure disclosed in Japanese Patent Laid-Open Publication No. 2005-209538 may require a large and complex attachment structure for a large radiator, as well as a space for attaching the large radiator. This means that the depth of the LED light source may be 100 mm or larger, and therefore, the entire united light source may be made larger and heavier. With respect to design considerations, it is difficult to use such a lamp as a vehicle lighting device, for example, as a rear light which is required to be relatively thin.
Various vehicle lighting devices that use an LED light source include direct-emission types in which the LED light source functions as a point source. When a vehicle lighting device employs a plurality of such LED light sources, light emitted from the lighting device may result in a granular sense to viewers. A vehicle lighting device in which light emitted from an LED light source can be diffused by a reflector or a lens cut to serve as a surface light source device.
Accordingly, there has been great difficulty in developing a vehicle lighting device that uses an LED as a light source and which has a linear light emission part with a narrow width.
In particular, a typical center high mount stop light is generally located on a rear window, and should have a vertical dimension (vertical width) as narrow as possible in order to ensure a rear field of view. When configuring such a linear light source using LEDs, a plurality of LEDs is typically arranged in line. Accordingly, the vertical width is approximately in the range of 15 mm to 20 mm. When configuring a linear light source, if the vertical width is required to be narrower, it may be necessary to cover the upper and lower areas of the light source, thereby disadvantageously shielding light from these areas. This may deteriorate the light take-out efficiency of the LEDs. Therefore, in order to obtain a linear light source utilizing an LED light source, this technique has not yet been realized or efficiently developed.